This invention relates to the method of in-line forming of integral fasteners with film or sheet stock to be made into bags or other containers which are reclosable by the fastener elements. It is parcticularly directed to a cast process wherein a single film and sheet carries more than one pair of fastener elements such as illustrated, for example, in FIG. 3 of U.S. Pat. No. 4,295,919. In the invention of U.S. Pat. No. 4,295,919, a pair of male elements are located in the central section of the sheet and female elements are located adjacent opposite edges of the sheet. In some cases, the film between the center two fasteners is thickened. When the film is slit between the fasteners, the thickened film becomes the lip that is grasped to open the bag. The thickened lip resists tearing when the bag is opened. When the film is thickened between the fasteners, they converge as they travel from the die to the chill roll. The lateral translation of each center fastener causes it to tip. To compensate for this tipping,fasteners in the past have been pre-tipped at the die.
Earlier methods designed at splitting the film web to accomplish the same purpose were not satisfactory, such slitting of the film web ocurring away from the die. Such remote slitting permitted the two center fastener elements to move together as they travelled from the die to the chill roll in response to lateral forces associated with lateral stress. This lateral movement of the fasteners in turn caused them to tip.
The pre-tipping solution has not been fully satisfactory in that the degree of necessary pre-tipping cannot accurately be anticipated, particularly with varying resins and process conditions, and cannot be adjusted responsively once the pre-tipping attitude is die cut into the die-plates. Failure to have the male profile in the proper attitude can result in unsatisfactory or less than totally satisfactory performance of the fastener elements forming the closure. Also, in such an arrangement, particularly where there is a base under a closure profile, a thinning of the film occurs adjacent the profile, which could result in unwanted film tearing.